The present invention relates to mechanisms for operating a choke of the carburetor on an internal combustion engine; and more particularly to a thermostatic control for such operating mechanisms.
Internal combustion engines conventionally include a system which provides fuel to the engine at a rate which varies in response to one or more operating conditions, such as the rate of air flow to the engine or a combination of engine speed and load. At each engine operating point, under normal operating temperatures, the fuel flow is carefully controlled to produce the desired engine torque.
During operation below normal operating temperatures, that same fuel flow rate may be insufficient to produce the torque required for the particular engine operating point. Accordingly, such engines conventionally include a choke or other mechanism to increase fuel flow and enrich the air-fuel mixture during low temperature operation. A sufficiently enriched air-fuel mixture assures that the engine produces adequate torque during the warm-up period before reaching the normal operating temperature range.
It has been recognized that an enriched air-fuel mixture increases fuel consumption and contributes to emission of hydrocarbons and carbon monoxide in the engine exhaust gases. Thus, in order to minimize those deleterious effects, prior cold temperature enrichment mechanisms scheduled the amount of enrichment with time, engine temperature and other engine operating conditions. Yet any such schedule is only an approximation of the cold enrichment actually required. When the cold enrichment schedule falls short of the required amount, the engine will produce insufficient torque; whereas when the schedules exceeds the required amount, the engine consumes unnecessary fuel and creates excessive exhaust emissions.
One common mechanism for controlling the choke as a function of operating temperature is a bimetallic helical spring. The device is a lamination of two metals with different coefficients of expansion, which cause the spring to curl into a tighter helix with temperature decreases and uncurl as the temperature increases. By attaching one end of the spring to the choke, the choke opens and closes with spring movement in correspondence with temperature, as described in U.S. Pat. No. 3,494,598.
Other choke control mechanisms directly connected different types of powered drivers to the carburetor choke along with the bimetallic spring thermostat to further refine the enrichment schedule to match the precise engine requirements. One of these mechanisms is shown in U.S. Pat. No. 4,321,902 in which separate linkages couple a motor and a bimetallic helical spring to the choke plate of the carburetor. The U.S. Pat. No. 4,768,478 describes using both a spring thermostat and an electric solenoid to control the position of the choke valve.